Activity component

An important industrial example of W/O emulsions arises in water-in-crude-oil emulsions that form during production. These emulsions must be broken to aid transportation and refining [43]. These suspensions have been extensively studied by Sjoblom and co-workers [10, 13, 14] and Wasan and co-workers [44]. Stabilization arises from combinations of surface-active components, asphaltenes, polymers, and particles the composition depends on the source of the crude oil. Certain copolymers can mimic the emulsion stabilizing fractions of crude oil and have been studied in terms of their pressure-area behavior [45]. 

RESOLUTION OF sec.-OCTYL ALCOHOL (d/-2-OCTA-NOL) INTO ITS OPTICALLY ACTIVE COMPONENTS (d- AND f-2-OCTANOL)... 

Film Rupture. Another general mechanism by which foams evolve is the coalescence of neighboring bubbles via film mpture. This occurs if the nature of the surface-active components is such that the repulsive interactions and Marangoni flows are not sufficient to keep neighboring bubbles apart. Bubble coalescence can become more frequent as the foam drains and there is less Hquid to separate neighbors. Long-Hved foams can be easHy... 

Process Rationale. The products of plasma fractionation must be both safe and efftcaceous, having an active component, protein composition, formulation, stabiUty, and dose form appropriate to the intended clinical appHcation. Processing must address a number of specific issues for each product. Different manufacturers may choose a different set or combination of unit operations for this purpose. 

ASA appears to be the active component of sulfasalazine without the sulfa component, and is free of the serious side effects seen with sulfasalazine. It is used orally, in a delay-release formulation, as a retention enema, and as a suppository. It is well tolerated in most patients. 

Manufacturing. The highly reactive nature of the active components of the permanent waving products requires rigorous control at every... 

National Agricultural Library database general coverage of U.S. agriculture active components of agrochemicals... 

Extracts of corpora lutea were known ia the early tweatieth ceatury to inhibit ovulatioa ia animals. Pure progesterone (3), the active component of the extracts, was isolated ia 1934 and its stmcture reported (15). Several problems limited its use and drove efforts to develop progesterone analogues, ie, it was available only ia small quantities from animal sources, was not orally active, and was discovered to cause androgenic side effects. 

Analytically, the inclusion phenomenon has been used in chromatography both for the separation of ions and molecules, in Hquid and gas phase (1,79,170,171). Peralkylated cyclodextrins enjoy high popularity as the active component of hplc and gc stationary phases efficient in the optical separation of chiral compounds (57,172). Chromatographic isotope separations have also been shown to occur with the help of Werner clathrates and crown complexes (79,173). 

At this writing anticholinergic agents are not widely used for the symptomatic treatment of asthma, although compounds such as atropine [51 -55-8] C17H23NO3, (18) have been used for centuries (111). Inhalation of the smoke produced by burning herbal mixtures, such as Datura Stramonium provided bronchodilation and rehef from some of the symptoms of asthma. The major active component in these preparations was atropine or other closely related alkaloids (qv). 

Eor virtually all radiopharmaceuticals, the primary safety consideration is that of radiation dosimetry. Chemical toxicity, although it must be considered, generally is a function of the nonradio active components of the injectate. These are often unreacted precursors of the intended radioactive product, present in excess to faciUtate the final labeling reaction, or intended product labeled with the daughter of the original radioactive label. 

Chiral separations have become of significant importance because the optical isomer of an active component can be considered an impurity. Optical isomers can have potentially different therapeutic or toxicological activities. The pharmaceutical Hterature is trying to address the issues pertaining to these compounds (155). Frequendy separations can be accompHshed by glc, hplc, or ce. For example, separation of R(+) and 5 (—) pindolol was accompHshed on a reversed-phase ceUulose-based chiral column with duorescence emission (156). The limits of detection were 1.2 ng/mL of R(+) and 4.3 ng/mL of 3 (—) pindolol in semm, and 21 and 76 ng/mL in urine, respectively. 

Tolnaftate [2398-96-17, C H NOS, which is active against dermatophytes, is the active component ia another antifimgal powder it also contains cetylpyridinium chloride and talcum venetum. 

Nystatin has three biologically active components A, A, and A. Figure 1 depicts A. Squibb is the U.S. producer. 

Bosch and co-workers devised laboratory reactors to operate at high pressure and temperature in a recycle mode. These test reactors had the essential characteristics of potential industrial reactors and were used by Mittasch and co-workers to screen some 20,000 samples as candidate catalysts. The results led to the identification of an iron-containing mineral that is similar to today s industrial catalysts. The researchers recognized the need for porous catalytic materials and materials with more than one component, today identified as the support, the catalyticaHy active component, and the promoter. Today s technology for catalyst testing has become more efficient because much of the test equipment is automated, and the analysis of products and catalysts is much faster and more accurate. 

A few industrial catalysts have simple compositions, but the typical catalyst is a complex composite made up of several components, illustrated schematically in Figure 9 by a catalyst for ethylene oxidation. Often it consists largely of a porous support or carrier, with the catalyticaHy active components dispersed on the support surface. For example, petroleum refining catalysts used for reforming of naphtha have about 1 wt% Pt and Re on the surface of a transition alumina such as y-Al203 that has a surface area of several hundred square meters per gram. The expensive metal is dispersed as minute particles or clusters so that a large fraction of the atoms are exposed at the surface and accessible to reactants (see Catalysts, supported). 

CatalyticaHy Active Species. The most common catalyticaHy active materials are metals, metal oxides, and metal sulfides. OccasionaHy, these are used in pure form examples are Raney nickel, used for fat hydrogenation, and y-Al O, used for ethanol dehydration. More often the catalyticaHy active component is highly dispersed on the surface of a support and may constitute no more than about 1% of the total catalyst. The main reason for dispersing the catalytic species is the expense. The expensive material must be accessible to reactants, and this requires that most of the catalytic material be present at a surface. This is possible only if the material is dispersed as minute particles, as smaH as 1 nm in diameter and even less. It is not practical to use minute... 

Cost. The catalytically active component(s) in many supported catalysts are expensive metals. By using a catalyst in which the active component is but a very small fraction of the weight of the total catalyst, lower costs can be achieved. As an example, hydrogenation of an aromatic nucleus requires the use of rhenium, rhodium, or mthenium. This can be accomplished with as fittie as 0.5 wt % of the metal finely dispersed on alumina or activated carbon. Furthermore, it is almost always easier to recover the metal from a spent supported catalyst bed than to attempt to separate a finely divided metal from a liquid product stream. If recovery is efficient, the actual cost of the catalyst is the time value of the cost of the metal less processing expenses, assuming a nondeclining market value for the metal. Precious metals used in catalytic processes are often leased. 

Since catalyst activity is dependent on how much catalytically active surface is available, it is usually desirable to maximi2e both the total surface area of the catalyst and the active fraction of the catalytic material. It is often easier to enlarge the total surface area of the catalyst than to increase the active component s surface area. With proper catalyst design, however, it is possible to obtain a much larger total active surface area for a given amount of metal or other active material in a supported catalyst than can be achieved in the absence of a support. 

The performance of a catalyst often depends as much on the care and method of preparation as on the identity of the active components. This fact has been learned by many who have failed to obtain reproducibiUty among catalyst preparations ia the laboratory or have been responsible for quaUty assurance ia catalyst manufacture. Also, there are many examples of strong effects of trace impurities ia raw material or catalyst support on catalyst performance. 

---